Start blob store service synchronously.

Starting the service asynchronously is resulting in a
race condition when accessing a shared data structure.
We could add a lock to guard this data structure but
this is resulting in a slightly worse performance than
starting the service synchronously.

Bug: 194428627
Bug: 179687249
Test: treehugger verification
Change-Id: Ib4d610e8a221f94a3dcc8475371b4a05e5582149